# COMSOL Blog

## Free Surface Computations in Mixers and Rotating Machinery

##### Ed Fontes | January 26, 2016

The rotation of the impellers in a mixer or stirred reactor creates ripples on the liquid surface when the agitation is moderate. If the ripples are small in comparison to the height of the fluid in the vessel, the shape and height of the free surface can be explicitly calculated from the velocity field in a separate solution step. The latest version of the Mixer Module in COMSOL Multiphysics includes a Stationary Free Surface feature for such computationally inexpensive calculations.

### Simulate Three-Phase Flow with a New Phase Field Interface

##### Ed Fontes | December 16, 2015

In COMSOL Multiphysics version 5.2, the CFD and Microfluidics modules include a new fluid flow interface for modeling separated three-phase flow. The model behind this fluid flow interface accounts for surface tension between each pair of fluids, contact angles with the walls, as well as the density and viscosity of each of the fluids. The phase field method computes the shape of the interfaces between the three phases and also accounts for interactions with walls.

### Does the Current Flow Backwards Inside a Battery?

##### Ed Fontes | November 25, 2015

During the discharge of a battery, the current in the circuit flows from the positive to the negative electrode. According to Ohm’s law, this means that the current is proportional to the electric field, which says that current flows from a positive to negative electric potential. But what happens inside the battery? Does the current flow from negative to positive electric potential? This blog post explains the potential profile inside a battery during discharge and recharge.

### Intro to Optimizing Mixer Design by Creating an App

##### Ed Fontes | July 6, 2015

Since we released version 5.0 of the COMSOL Multiphysics® software, you have the ability to create simulation apps — either starting from scratch or with a demo app from the Application Library. Today, we’ll introduce you to an app that can be used for understanding and optimizing mixer design and operation for a given fluid. The exemplified application models and simulates stirred tank mixers, which are used for reactors in the fine chemical, pharmaceutical, food, and consumer products industries.

### Sensing the Bio in Biosensor Design with a Simulation App

##### Ed Fontes | May 12, 2015

Biosensors are the workhorses of the analytical tools used for detailed mechanistic understanding at the molecular level of biological systems. The applications of these analysis tools are countless for the detection of biomolecules in the pharmaceutical, health care, and food industries; agriculture; environmental technologies; and in general for research of biological systems. The biosensor demo app is a good example of an application where non-experts can benefit from accurate multiphysics simulations.

### Parallel Universes, Schrödinger, Hawking, Borges, and One Direction

##### Ed Fontes | May 7, 2015

What is the relation between the extremely popular band One Direction, quantum mechanics, and cosmology? Stephen Hawking may just have explained this relation in one of his recent talks at the Sydney Opera House. It has to do with the prediction of parallel universes, where we, in an infinite number of worlds, could find worlds that are almost identical to ours but with all possible permutations and differences, much like the 410-page books in The Library of Babel by Borges.

### Why Car Batteries Perform Poorly in Cold Weather

##### Ed Fontes | February 5, 2015

Starting the car on a cold winter morning can be unpleasant if you have not been proactive the night before. When you are unable to start an engine, it is often the battery’s fault. Why is a battery more sensitive than other processes in a car? The answer lies in the battery’s ability to convert chemical energy into electrical energy, with a minimum of heat generation, and the relatively small amounts of thermal energy available at low temperatures.

### Modeling Approaches in Heterogeneous Catalysis

##### Ed Fontes | February 3, 2015

Modeling of heterogeneous catalysis traditionally attracts great interest from the chemical engineering community, due to the many industrial processes that utilize this type of catalysis. Here, we discuss the procedure of starting with detailed micro-geometries and then proceeding with approximations through homogenization. By following this procedure, from the microscopic particle level to the macroscopic reactor level, we can design the catalyst in detail and study the influence of this design on the total reactor performance.

### Geometry Modeling in Simulation Apps

##### Ed Fontes | January 8, 2015

COMSOL applications created with the new Application Builder will make sophisticated simulations based on parameterized CAD models more accessible than ever before. A COMSOL application allows easy access to not only parameterized models but also completely different geometry configurations, such as a mixer with a variable number of impeller blades or a variable number of impellers. To make this easy for the application developer, we have made available cumulative selections and geometry parts. See how these tools work.

### Apps for Teaching Mathematical Modeling of Tubular Reactors

##### Ed Fontes | November 21, 2014

The Tubular Reactor application is a tool where students can model a nonideal tubular reactor, including radial and axial variations in temperature and composition, and investigate the impact of different operating conditions. It also exemplifies how teachers can build tailored interfaces for problems that challenge the students’ imagination. The model and exercise are originally described in Scott Fogler’s book Elements of Chemical Reaction Engineering. I wish I had access to this type of tool when I was a student!

### Sometimes a Cigar Is More Than Just a Cigar

##### Ed Fontes | September 10, 2014

As a chemical engineer, I can’t just smoke a cigar and leave it at that. Here, I investigate the anatomy, structure, and chemical process zones of a cigar and show you a simple model of the temperature distribution of the smoke in a cigar as well as the concentration of oxygen.